For safety travel of an automotive vehicle, the wheel support bearing assembly equipped with a sensor for detecting the rotational speed of one of automotive wheels has hitherto been well known in the art. While the automobile traveling safety precaution is hitherto generally taken by detecting the rotational speed of the wheel, but it is not sufficient with the detection of only the rotational speed of the wheel and, therefore, it is required to achieve an improved safety control with the use of other sensor signals.
In view of this, it may be contemplated to achieve an attitude control based on the detection of a load acting on each of wheels during travel of an automotive vehicle. By way of example, a large load acts on the outside wheels during the cornering, on the wheels on one side during the run along left and right inclined road surfaces or on the front wheels during the braking, and, thus, a varying load acts on the vehicle wheels. Also, even in the case of the uneven live load, the loads acting on those wheels tend to become uneven. For this reason, if the loads acting on the wheels can be detected as needed, suspension systems for the vehicle wheels can be controlled beforehand based on results of detection of the loads so that the attitude of the automotive vehicle during the traveling thereof (for example, prevention of a rolling motion during the cornering, prevention of downward settling of the front wheels during the braking, and prevention of downward settling of the vehicle wheels brought about by an uneven distribution of live loads) can be controlled. However, no space for installation of the load sensor for detecting the load acting on the respective vehicle wheel is available and, therefore, the attitude control through the detection of the load can hardly be realized.
Also, in the event that in the near future the steer-by-wire is introduced to provide the system in which the wheel axle and the steering come not to be coupled mechanically with each other, and such system is increasingly used, information on the road surface comes to be required to transmit to the steering wheel held by a driver by detecting a load acting in a wheel axis direction.
In order to meet those needs hitherto recognized, it has been suggested to use various sensors such as temperature sensor, vibration sensor and load sensor in the wheel support bearing assembly so that in addition to the rotational speed, various parameters useful for the travel of the automotive vehicle can be detected. (See, for example, the Japanese Laid-open Patent Publications No. 2004-45219 and No. 2004-198210.)
The first mentioned patent document No. 2004-45219 discloses the determination of the type of load, the direction of the load and the magnitude of the load by the utilization of signals provided for by eight displacement sensors for detection of a horizontal load Fx, an axial load Fy acting in a direction parallel to the axis of rotation, a vertical load Fz, a moment load Mx acting around a horizontal axis, a moment load My acting around a rotation axis and a moment load Mz acting around a vertical axis, all acting on the wheel support bearing assembly. Also, the second mentioned patent document No. 2004-198210 discloses, in combination with displacement sensors, the additional use of a separate sensor oriented in a radial direction or a thrust direction relative to the displacement sensors for the purpose of eliminating the effects of heat expansion and/or heat shrinkage of bearing elements due to the change in temperature.
However, the bearing assembly disclosed in any one of the above discussed patent documents requires the use of at least 12 sensors in order to determine those loads acting on the wheel support bearing assembly with high accuracy while the influences on the bearing elements brought about by the change in temperature are removed. Thus, the number of component parts (sensors) to be added for the measurement of those loads is increased and, therefore, it is unavoidable to increase the cost and the weight of the bearing assembly. Also, the use of the increased number of the sensors eventually results in increase of the size of a detecting circuit and/or a controller for those sensors, unnecessarily accompanied by increase of the cost and the weight. For those reasons, the bearing assembly disclosed in any one of the above discussed patent documents is ineffective to accomplish reduction in cost and weight, both of which have been desired for in the wheel support bearing assembly.